The present invention relates to electrodes of a vacuum circuit breaker and, more particularly, to electrodes of a vacuum circuit breaker having a high dielectric strength, large breaking current and a superior non-welding characteristic.
Electrodes of a circuit breaker has to have various electric and physical properties such as (1) high dielectric strength, (2) superior non-welding characteristic, (3) large breaking current, (4) small chopping current, (5) small gaseous content and so forth, among which the properties (1) to (3) are important factors which affects the breaking capacity of the vacuum circuit breaker.
The aforementioned properties can be improved to some extent by improving the electrode material or technic of production of the electrodes. It is, however, considerably difficult to simultaneously achieve the improvements in both of the dielectric strength and the breaking current characteristic.
Hitherto, an electrode having a high dielectric strength has been known, which is composed of an alloy comprising an iron group metal such as iron (Fe) or cobalt (Co) and remainder of copper (Cu). This electrode unfortunately has only a small breaking current, because it possesses a conductivity which is not greater than 30 IACS%.
Also, as an electrode having a large breaking current and superior non-welding characteristic, an electrode has been known which is composed of an alloy comprising a metal having a low melting point and high vapor pressure, as well as extremely small solid solubility to copper, e.g. lead (Pb), bismuth (Bi) or the like and remainder of copper (Cu). This electrode, however, exhibits an impractically low dielectric strength.
An electrode which is composed of an alloy comprising copper containing both of the aforementioned iron group metal and a metal of low melting point and high vapor pressure such as Pb and Bi has been known also. This electrode exhibits unexpectedly a breaking current the level of which is as low as that of the electrode which is composed of an alloy comprising the iron group metal and the Cu.
An electrode made of an alloy comprising Cu and a rare earth metal has been known as an electrode which exhibits a property intermediate of those of the electrode having the high dielectric strength and the electrode having the large breaking current. Some of the electrodes of this kind is formed as a compound of Cu and the rare earth metal. This electrode, however, is poor in the non-welding characteristic which is another essential requisite for the vacuum circuit breaker. Namely, the electrodes of this material are liable to be welded to each other by a certain breaking current.
Meanwhile, a current tendency of enlargement of the capacity of incoming facilities and substations gives a rise to a demand for an electrode material which possesses all of the essential requisites (1) to (3), i.e. high dielectric strength, large breaking current and superior non-welding characteristic.
The fourth requisite, i.e. the small chopping current, can be achieved by adding various metals to the matrix material. However, recently, the problem concerning the chopping current is becoming less severe, because of various measures taken in the electric circuit for suppressing the extraordinary voltage which would cause a large chopping current. The fifth requisite, i.e. small gaseous content, can be achieved by making an ingot of the electrode material in a vacuum atmosphere making use of de-gassing material or the like measure.